Rotor

The present invention relates to a rotor for a wind or water power machine, the rotor including a hub, supported by a main shaft, and a blade, a root end of the blade being connected to the hub.

In a conventional example of a rotor for a wind power generator, the leading edge of the blade is formed to be linear across nearly the entire length of the leading edge (for example, Patent Literature 1).

Patent Literature

PTL 1: JP 2006-132542 A

Technical Problem

In general, when the rotor for a wind power generator rotates, a vortex is generated near the leading edge of the blade due to the flow of wind (air), i.e. fluid, near the surface of the blade and to centrifugal force. This vortex flows across the leading edge of the blade outward in the radial direction of the rotor from near the end of the leading edge that is inward in the radial direction of the rotor. In the rotor disclosed in Patent Literature 1, such a vortex flows across the leading edge of the blade outward in the radial direction of the rotor from near the end of the leading edge that is inward in the radial direction of the rotor, yet the vortex sometimes separates from the surface of the blade and disintegrates just before reaching near the end that is outward in the radial direction of the rotor. Fluid resistance increases due to such disintegration of the vortex, causing the problems of increased noise and a reduction in power generation efficiency.

The present invention has been conceived to resolve these problems and provides a rotor for a wind or water power machine, the rotor reducing the fluid resistance experienced by the blade.

Solution to Problem

The main structure of the present invention for resolving these problems is as follows.

A rotor according to the present invention is for a wind or water power machine, the rotor comprising a hub, supported by a main shaft, and a blade, a root end of the blade being connected to the hub, wherein in a projection plane perpendicular to a central axis of rotation of the rotor, at least a portion of a leading edge of the blade protrudes forward in a rotational direction of the rotor with respect to a first line segment connecting an inward end of the leading edge in a radial direction of the rotor and an outward end of the leading edge in the radial direction of the rotor, and a tip of a leading edge protrusion is positioned outward in the radial direction of the rotor from a peripheral edge of the hub by a distance of 0.4 to 0.6 times a length of the blade, and at least a portion of a section of the leading edge of the blade extending from the inward end of the leading edge in the radial direction of the rotor to the tip of the leading edge protrusion is curved or bent to be convex backward in the rotational direction of the rotor with respect to a second line segment connecting the inward end of the leading edge in the radial direction of the rotor and the tip of the leading edge protrusion.

According to the rotor of the present invention, when the rotor rotates, the vortex generated near the leading edge of the blade is generated along the leading edge across the entire length thereof, and near the tip of the leading edge protrusion, the vortex can be split in two parts that act to cancel each other out. As a result, the vortex that is generated near the leading edge can be weakened, and the fluid resistance experienced by the blade can be reduced.

In the present invention, a “wind or water power machine” refers to any machine that uses the motive power obtained by fluid force, e.g. wind power, water power, or the like, such as a wind power generator (including a wave power generator that uses air flow and the like; the same holds below), a water power generator (including a tidal power generator, an ocean current power generator, and the like; the same holds below), or the like.

The “length of the blade” in the present invention refers to the radius of the rotor minus the radius of the hub. The “radius of the rotor” refers to the distance from the central axis of rotation of the rotor to the outermost edge of the blade in the radial direction of the rotor. When the hub does not have a circular shape in a projection plane perpendicular to the central axis of rotation of the rotor, the “radius of the hub” refers to the radius of a circumscribed circle of the hub in the projection plane.

In the projection plane, the “tip of the leading edge protrusion” in the present invention refers to a point, among points on the leading edge of the blade that are located forward in the rotational direction of the rotor with respect to the first line segment, yielding the maximum distance between the point and the intersection of the first line segment with a perpendicular from the point to the first line segment.

Furthermore, “curved or bent” in the present invention refers to extending in a shape in which one or more arcs and/or lines are connected.

In the rotor according to the present invention, in a projection plane perpendicular to a central axis of rotation of the rotor, at least a portion of a trailing edge of the blade preferably protrudes forward in the rotational direction of the rotor with respect to a third line segment connecting an inward end of the trailing edge in the radial direction of the rotor and an outward end of the trailing edge in the radial direction of the rotor, and a tip of a trailing edge protrusion is preferably positioned outward in the radial direction of the rotor from the peripheral edge of the hub by a distance of 0.4 to 0.6 times the length of the blade, and at least a portion of a section of the trailing edge of the blade extending from the inward end of the trailing edge in the radial direction of the rotor to the tip of the trailing edge protrusion is preferably curved or bent to be convex backward in the rotational direction of the rotor with respect to a fourth line segment connecting the inward end of the trailing edge in the radial direction of the rotor and the tip of the trailing edge protrusion.

According to this structure, the shape of the trailing edge of the blade can be formed to follow the shape of the leading edge, thereby preventing the friction drag on the surface of the blade from becoming excessively large in at least a portion at the width center line of the blade.

In the projection plane, the “tip of the trailing edge protrusion” in the present invention refers to a point, among points on the trailing edge of the blade that are located forward in the rotational direction of the rotor with respect to the third line segment, yielding the maximum distance between the point and the intersection of the third line segment with a perpendicular from the point to the third line segment.

In the rotor according to the present invention, in a projection plane perpendicular to a central axis of rotation of the rotor, at least a portion of a section of the leading edge of the blade extending from the tip of the leading edge protrusion to the outward end of the leading edge in the radial direction of the rotor preferably protrudes forward in the rotational direction of the rotor with respect to a fifth line segment connecting the tip of the leading edge protrusion and the outward end of the leading edge in the radial direction of the rotor.

This structure can reduce the air resistance further.

Another rotor according to the present invention is a rotor for a wind or water power machine comprising a hub, supported by a main shaft, and a blade, a root end of the blade being connected to the hub, wherein in a projection plane perpendicular to a central axis of rotation of the rotor, at least a portion of a leading edge of the blade protrudes forward in a rotational direction of the rotor with respect to a first line segment connecting an inward end of the leading edge in a radial direction of the rotor and an outward end of the leading edge in the radial direction of the rotor, at least a portion of a section of the leading edge of the blade extending from the inward end of the leading edge in the radial direction of the rotor to a tip of a leading edge protrusion is curved or bent to be convex forward in the rotational direction of the rotor with respect to a second line segment connecting the inward end of the leading edge in the radial direction of the rotor and the tip of the leading edge protrusion, and at least a portion of a section of the leading edge of the blade extending from the tip of the leading edge protrusion to the outward end of the leading edge in the radial direction of the rotor protrudes backward in the rotational direction of the rotor with respect to a fifth line segment connecting the tip of the leading edge protrusion and the outward end of the leading edge in the radial direction of the rotor.

According to the rotor of the present invention, the fluid resistance experienced by the blade can be reduced.

In the other rotor according to the present invention, in a projection plane perpendicular to a central axis of rotation of the rotor, at least a portion of a trailing edge of the blade preferably protrudes forward in the rotational direction of the rotor with respect to a third line segment connecting an inward end of the trailing edge in the radial direction of the rotor and an outward end of the trailing edge in the radial direction of the rotor.

According to this structure, the shape of the trailing edge of the blade can be formed to follow the shape of the leading edge, thereby preventing the friction drag on the surface of the blade from becoming excessively large in at least a portion at the width center line of the blade.

In the rotor or the other rotor according to the present invention, in a projection plane perpendicular to a central axis of rotation of the rotor, a tip portion of the blade outward in the radial direction of the rotor preferably comprises a plurality of branched portions, each of the branched portions preferably tapers off outward in the radial direction of the rotor, and a portion of the leading edge and a portion of a trailing edge of the blade along the branched portions preferably extend along respective tangent lines to the leading edge and the trailing edge at branch starting positions of the branched portions.

According to this structure, in usage conditions such that laminar flow occurs, the vortex generated near the tip portion of the blade when the rotor rotates can be weakened, thereby further reducing the fluid resistance.

In the rotor or the other rotor according to the present invention, in a projection plane perpendicular to a central axis of rotation of the rotor, a plurality of extended portions is preferably provided along the leading edge, the extended portions extending forward in the rotational direction of the rotor from the leading edge of the blade and tapering off forward in the rotational direction of the rotor, and a tip portion of the blade outward in the radial direction of the rotor preferably tapers off outward in the radial direction of the rotor.

According to this structure, mainly in usage conditions such that turbulent flow occurs, the occurrence of turbulent flow near the leading edge of the blade can be suppressed, and the generation of a vortex near the tip portion of the blade can also be suppressed. Therefore, in the above case, the fluid resistance can be reduced further.

In the rotor or the other rotor according to the present invention, a plurality of projections each having a height and diameter of 5 mm or less is preferably formed in a region at least on a leading edge side of a surface of the blade at a front side of the rotor.

According to this structure, turbulent flow occurring mainly near the region on the leading edge side of the surface of the blade at the front side of the rotor can be weakened, and the fluid resistance experienced by the blade can be further reduced.

The “diameter” of the projections in the present invention refers to the diameter of a circumscribed circle of each projection in a projection plane perpendicular to the central axis of rotation of the rotor.

In the rotor or the other rotor according to the present invention, the number of the projections per unit area on the surface of the blade at least at the front side of the rotor preferably decreases from the leading edge towards the trailing edge of the blade.

According to this structure, while weakening the turbulent flow occurring mainly near the region on the leading edge side of the surface of the blade at the front side of the rotor, if the turbulent flow also occurs near or advances to another surface region of the blade, such turbulent flow can be weakened, thereby further reducing the fluid resistance experienced by the blade.

In the present invention, stating that the number of the projections per unit area on the surface of the blade “decreases” from the leading edge towards the trailing edge of the blade refers to the number of the projections per unit area on the surface of the blade decreasing with one or more locations as borders or decreasing gradually from the leading edge towards the trailing edge of the blade.

Advantageous Effect of Invention

According to the present invention, it is possible to provide a rotor for a wind or water power machine that can reduce the fluid resistance experienced by the blade.

The present invention will be further described below with reference to the accompanying drawings, wherein:

FIG. 1 is a front view illustrating Embodiment 1 of a rotor according to the present invention;

FIG. 2 is a front view illustrating the main parts of the rotor in FIG. 1 ;

FIG. 3 is a cross-section along the A-A line in the width direction of the blade in FIG. 2 ;

FIG. 4 is a front view illustrating Embodiment 1 of another rotor according to the present invention;

FIG. 5 is a front view illustrating the main parts of a rotor according to Embodiment 2 of the present invention; and

FIG. 6 is a front view illustrating Embodiment 2 of another rotor according to the present invention.

The following describes embodiments of the present invention in detail with reference to the drawings.

Embodiment 1 of the present invention is described with reference to FIGS. 1 to 3 . FIG. 1 is a front view illustrating Embodiment 1 of a rotor according to the present invention. FIG. 2 is a front view illustrating the main parts of the rotor 1 A in FIG. 1 . The rotor 1 A in FIG. 1 is used in a wind power generator. The diameter φ A of the rotor 1 A is 2 m, the number of revolutions at a wind speed of 5 m/s to 20 m/s is 10 rpm to 50 rpm, and the output is 1 kW to 2 kW. It is assumed that the rotor 1 A is used in a laminar flow region with a Reynolds number of 100,000 or less. The rotor 1 A according to the present embodiment, however, can be used not only in a wind power generator but also in a water power generator or another wind or water power machine. The diameter φ A of the rotor 1 A is preferably 5 m or less, more preferably 0.2 m or more, and even more preferably 0.5 m or more.

The rotor 1 A includes a hub 10 A, supported by a main shaft (not illustrated), and three blades 20 A, a root end 21 A of each blade 20 A being connected to the hub 10 A. When looking at FIG. 1 , the non-illustrated main shaft extends backwards from the back side of the hub 10 A and is provided horizontally in this example. The hub 10 A is supported by the main shaft so that the main shaft and the central axis of rotation O of the rotor 1 A are aligned.

The number of blades 20 A is not limited to three and may be any number.

The blade illustrated in FIGS. 2 and 3 is used for each blade 20 A of the rotor 1 A, yet it is also possible to use the blade illustrated in FIGS. 2 and 3 for only a portion of the blades 20 A.

In the example in FIG. 2 , in a projection plane perpendicular to the central axis of rotation O of the rotor 1 A (i.e. in the plane of FIG. 2 ), the leading edge 31 A of the blade 20 A protrudes forward in the rotational direction RD (counterclockwise in FIG. 2 ) of the rotor 1 A across the entire length of the leading edge 31 A with respect to a first line segment L 1A , connecting an inward end 33 A of the leading edge 31 A in the radial direction of the rotor 1 A and an outward end 35 A of the leading edge 31 A in the radial direction of the rotor 1 A. While not illustrated, in the projection plane, the leading edge 31 A of the blade 20 A may alternatively protrude forward in the rotational direction RD of the rotor 1 A with respect to the first line segment L 1A across only a portion of the leading edge 31 A.

In the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, in the example in FIG. 2 , the tip 32 A of the leading edge protrusion, with respect to the first line segment L 1A , in the leading edge 31 A of the blade 20 A is positioned outward in the radial direction of the rotor 1 A from the peripheral edge of the hub 10 A by a distance of 0.4 to 0.6 times the length BL A of the blade 20 A. In other words, as illustrated in FIG. 2 , the tip 32 A of the leading edge protrusion is positioned within a radial direction region C A of the rotor 1 A that is 0.4 to 0.6 times the length BL A of the blade 20 A from the peripheral edge of the hub 10 A. In this case, as described above, the length BL A of the blade 20 A refers to the radius of the rotor 1 A (φ A /2) minus the radius r A of the hub 10 A. The radius of the rotor 1 A (φ A /2) refers to the distance from the central axis of rotation O of the hub 10 A to the outermost edge of the blade 20 A in the radial direction of the rotor 1 A. In the present example, the tip 32 A of the leading edge protrusion is preferably positioned outward in the radial direction of the rotor 1 A from the peripheral edge of the hub 10 A by a distance of 0.47 to 0.57 times the length BL A of the blade 20 A and more preferably by a distance of 0.51 to 0.53 times the length BL A of the blade 20 A.

According to this structure of the leading edge 31 A, when the rotor 1 A rotates and a vortex is generated near the leading edge 31 A of the blade 20 A, disintegration of the vortex near the outward end of the blade 20 A in the radial direction of the rotor 1 A can be suppressed, and the vortex can be generated along the leading edge 31 A across the entire length of the leading edge 31 A. The vortex generated along the leading edge 31 A of the blade 20 A is split in two parts near the tip 32 A of the leading edge protrusion. Therefore, the vortex that is further inward in the radial direction of the rotor 1 A than the tip 32 A of the leading edge protrusion and the vortex that is further outward in the radial direction of the rotor 1 A than the tip 32 A of the leading edge protrusion act to cancel each other out. As a result, the vortex that is generated near the leading edge 31 A can be weakened, and the air resistance experienced by the blade 20 A can be reduced.

From the perspective of weakening the above-described vortex generated near the leading edge 31 A, the angle θ 1A between a second line segment L 2A connecting the inward end 33 A of the leading edge 31 A in the radial direction of the rotor 1 A and the tip 32 A of the leading edge protrusion and a fifth line segment L 5A connecting the outward end 35 A of the leading edge 31 A in the radial direction of the rotor 1 A and the tip 32 A of the leading edge protrusion is preferably 145° to 155° and more preferably 147° to 153°.

In the example in FIG. 2 , in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, a majority of a section 34 A of the leading edge 31 A of the blade 20 A extending from the inward end 33 A of the leading edge 31 A in the radial direction of the rotor 1 A to the tip 32 A of the leading edge protrusion (also referred to as the “section of the leading edge 31 A inward in the radial direction of the rotor 1 A”) is curved to be convex backward in the rotational direction RD of the rotor 1 A with respect to the second line segment L 2A connecting the inward end 33 A of the leading edge 31 A in the radial direction of the rotor 1 A and the tip 32 A of the leading edge protrusion. It suffices, however, for at least a portion of the section 34 A of the leading edge 31 A inward in the radial direction of the rotor 1 A to be curved or bent backward in the rotational direction RD of the rotor 1 A with respect to the second line segment L 2A . The section 34 A may also be similarly curved or bent across the entire length thereof.

According to this structure of the section 34 A of the leading edge 31 A inward in the radial direction of the rotor 1 A, as compared to when the section 34 A extends along the second line segment L 2A , a vortex can be generated to flow even better along the section 34 A due to the flow of wind near the section 34 A and to centrifugal force when the rotor 1 A rotates. As a result, the air resistance experienced by the blade 20 A can be reduced.

In the example in FIG. 2 , the trailing edge 41 A of the blade 20 A also has the same structure as the above-described leading edge 31 A. In other words, in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, at least a portion (the entirety in the illustrated example) of the trailing edge 41 A of the blade 20 A protrudes forward in the rotational direction RD of the rotor 1 A with respect to a third line segment L 3A connecting an inward end 43 A of the trailing edge 41 A in the radial direction of the rotor 1 A and an outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A. Furthermore, the tip 42 A of the trailing edge protrusion, with respect to the third line segment L 3A , in the trailing edge 41 A is positioned outward in the radial direction of the rotor 1 A from the peripheral edge of the hub 10 A by a distance of 0.4 to 0.6 times, preferably 0.47 to 0.57 times, and more preferably 0.51 to 0.53 times the length BL A of the blade 20 A.

As illustrated in FIG. 2 , when at least a portion of the section 34 A extending from the inward end 33 A of the leading edge 31 A of the blade 20 A in the radial direction of the rotor 1 A to the tip 32 A of the leading edge protrusion is curved or bent to be convex backward in the rotational direction of the rotor 1 A with respect to the second line segment L 2A , then at least a portion (the entirety in the illustrated example) of a section 44 A extending from the inward end 43 A of the trailing edge 41 A in the radial direction of the rotor 1 A to the tip 42 A of the trailing edge protrusion is preferably curved or bent to be convex backward in the rotational direction RD of the rotor 1 A with respect to a fourth line segment L 4A connecting the inward end 43 A of the trailing edge 41 A in the radial direction of the rotor 1 A and the tip 42 A of the trailing edge protrusion. According to this structure of the trailing edge 41 A of the blade 20 A, the trailing edge 41 A can be formed to follow the shape of the leading edge 31 A. Hence, in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, the width of the blade 20 A can be prevented from becoming excessively large in at least a portion at the width center line (the alternate long and short dash line in FIG. 1 ) of the blade 20 A. The friction drag on the surface of the blade 20 A can thus be prevented from becoming excessively large in at least a portion at the width center line of the blade 20 A.

Like the leading edge 31 A, from the perspective of reducing air resistance, the angle θ 2A between the fourth line segment L 4A connecting the inward end 43 A of the trailing edge 41 A in the radial direction of the rotor 1 A and the tip 42 A of the trailing edge protrusion and a sixth line segment L 6A connecting the outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A and the tip 42 A of the trailing edge protrusion is preferably 145° to 155° and more preferably 147° to 153°.

As illustrated in FIG. 2 , in a projection plane perpendicular to the central axis of rotation O of the rotor 1 A, when at least a portion of the section 34 A extending from the inward end 33 A of the leading edge 31 A of the blade 20 A in the radial direction of the rotor 1 A to the tip 32 A of the leading edge protrusion is curved or bent to be convex backward in the rotational direction of the rotor 1 A with respect to the second line segment L 2A , then at least a portion (the entirety in the illustrated example) of a section 37 A extending from the tip 32 A of the leading edge protrusion to the outward end 35 A in the radial direction of the rotor 1 A is preferably curved or bent to be convex forward in the rotational direction RD of the rotor 1 A with respect to the fifth line segment L 5A connecting the tip 32 A of the leading edge protrusion and the outward end 35 A of the leading edge 31 A in the radial direction of the rotor 1 A. According to this structure, a vortex can be generated to flow even better along the section 37 A due to the flow of wind near the section 37 A and to centrifugal force when the rotor 1 A rotates. As a result, the air resistance can be reduced further.

When at least a portion (the entirety in the illustrated example) of the section 37 A extending from the tip 32 A of the leading edge protrusion of the blade 20 A to the outward end 35 A in the radial direction of the rotor 1 A is curved or bent to be convex forward in the rotational direction RD of the rotor 1 A with respect to the fifth line segment L 5A , then from the perspective of reducing air resistance, at least a portion (the entirety in the illustrated example) of a section 47 A extending from the tip 42 A of the trailing edge protrusion to the outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A is preferably curved or bent to be convex forward in the rotational direction RD of the rotor 1 A with respect to the sixth line segment L 6A , connecting the tip 42 A of the trailing edge protrusion and the outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A.

In the example in FIG. 2 , in a projection plane perpendicular to the central axis of rotation O of the rotor 1 A, a tip portion of the blade 20 A outward in the radial direction of the rotor 1 A branches into a plurality of branched portions 51 A. Each of the branched portions 51 A tapers off outward in the radial direction of the rotor 1 A.

Furthermore, in the example in FIG. 2 , along the branched portions 51 A, portions 36 A, 46 A of the leading edge 31 A and the trailing edge 41 A of the blade 20 A along the branched portions 51 A extend along respective tangent lines l 1 , l 2 to the leading edge 31 A and the trailing edge 41 A at branch starting positions R, S of the branched portions 51 A.

The branch starting position R of the branched portion 51 A on the leading edge 31 A refers to the intersection between the leading edge 31 A and a perpendicular to the leading edge 31 A from a back end P, in the rotational direction RD of the rotor 1 A, of the branched portion 51 A positioned furthest forward, among the branched portions 51 A, in the rotational direction RD of the rotor 1 A. The portion 36 A of the leading edge along the branched portion 51 A refers to the portion extending linearly from the branch starting position R of the leading edge 31 A to the outward end 35 A in the radial direction of the rotor 1 A.

Similarly, the branch starting position Q of the branched portion 51 A on the trailing edge 41 A refers to the intersection between the trailing edge 41 A and a perpendicular to the trailing edge 41 A from a front end Q, in the rotational direction RD of the rotor 1 A, of the branched portion 51 A positioned furthest backward, among the branched portions 51 A, in the rotational direction RD of the rotor 1 A. The portion 46 A of the trailing edge along the branched portion 51 A refers to the portion extending linearly from the branch starting position S of the trailing edge 41 A to the outward end 45 A in the radial direction of the rotor 1 A.

According to this structure of the tip portion of the blade 20 A outward in the radial direction, when the rotor 1 A rotates, the vortex generated near the tip portion of the blade 20 A can be weakened. As a result, the air resistance can be reduced further.

In the example in FIG. 2 , in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, the shape, direction of extension, and length of extension of each of the branched portions 51 A are nearly identical, yet the branched portions 51 A may have a different direction of extension and/or length of extension.

The direction of extension and length of extension of a branched portion 51 A refer to the direction of extension and length of extension of a line segment that connects the outward end of the branched portion 51 A in the radial direction of the rotor 1 A and intermediate points between the front end and the back end of the branched portion 51 A in the rotational direction RD of the rotor 1 A. The direction of extension and length of extension of the branched portions 51 A that are furthest to the front and the back in the rotational direction RD of the rotor 1 A, however, refer to the direction of extension and length of extension of the portions 36 A, 46 A, along the branched portions 51 A, of the leading edge 31 A and the trailing edge 41 A.

In the projection plane, the shape of each branched portion 51 A is approximately triangular in FIG. 2 , yet as long as the branched portions 51 A taper off outward in the radial direction of the rotor 1 A, they may be of any shape, such as an approximate Gaussian curve or approximately trapezoidal. In the projection plane, the branched portions 51 A are not limited to being connected to each other as in the example in FIG. 2 . While not illustrated, the branched portions 51 A may be separated from each other.

It is preferable, from the perspective of reducing air resistance, for the directions of extension of the branched portions 51 A to change gradually and smoothly from one branched portion 51 A to the next between the forward-end branched portion 51 A and the backward-end branched portion 51 A in the rotational direction RD of the rotor 1 A.

In the example in FIG. 2 , the directions of extension of the branched portions 51 A are approximately parallel to each other. Instead of the structure in the example in FIG. 2 , however, with increasing distance outward in the radial direction of the rotor 1 A, the directions of extension of the branched portions 51 A from the branched portion 51 A furthest forward to the branched portion 51 A furthest back in the rotational direction RD of the rotor 1 A more preferably extend in directions that separate from each other and change gradually and smoothly from one branched portion 51 A to the next. With this structure, when the rotor 1 A rotates, the vortex that is generated near the tip portion of the blade 20 A can be caused to flow more smoothly outward in the radial direction of the rotor 1 A and backward in the rotational direction RD. Air resistance can thus be further reduced.

In the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, the outward end 35 A of the leading edge 31 A in the radial direction of the rotor 1 A and the outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A need not lie on the same circle having the central axis of rotation O of the rotor 1 A as the center.

FIG. 3 is a cross-section along the A-A line in the width direction of the blade 20 A in FIG. 2 . While not illustrated in FIGS. 1 and 2 , a plurality of projections 50 is formed on the surface of the blade 20 A, as illustrated in FIG. 3 , thereby providing the surface of the blade 20 A with unevenness approximately like that of rough skin. In this context, the surface of the blade 20 A refers to both the surface of the blade 20 A at the front side of the rotor 1 A (i.e. the front of FIG. 1 ) and the surface of the blade 20 A at the back side of the rotor 1 A (i.e. the back of FIG. 1 ).

The height h and diameter d of the projection 50 illustrated in the partial enlargement in FIG. 3 are preferably each 5 mm or less and more preferably 3 mm or less. Considering the cost of surface treatment for the blade 20 A, the height h and diameter d of each projection 50 are preferably at least 0.001 mm and more preferably at least 0.01 mm.

In the example in FIG. 3 , the projections 50 are formed over nearly the entire surface of the blade 20 A. The number of projections 50 per unit area on the surface of the blade 20 A at the front side of the rotor 1 A decreases from the leading edge 31 A towards the trailing edge 41 A of the blade 20 A. Specifically, in the example in FIG. 3 , the number of projections 50 per unit area on the surface of the blade 20 A at the front side of the rotor 1 A decreases from the leading edge 31 A towards the trailing edge 41 A of the blade 20 A with one location (the position of the alternate long and two short dashes line in FIG. 3 ) as a border. Therefore, on the surface of the blade 20 A at the front side of the rotor 1 A, the number of projections 50 per unit area in a region on the leading edge 31 A side is greater than the number of projections 50 per unit area in a region on the trailing edge 41 A side.

While not illustrated, the number of projections 50 per unit area on the surface of the blade 20 A at the front side of the rotor 1 A may decrease from the leading edge 31 A towards the trailing edge 41 A of the blade 20 A with a plurality of locations as borders or may decrease gradually.

Furthermore, in the example in FIG. 3 , the number of projections 50 per unit area on the surface of the blade 20 A at the back side of the rotor 1 A is approximately constant from the leading edge 31 A to the trailing edge 41 A of the blade 20 A and is equivalent to the number in the region at the trailing edge 41 A side on the surface at the front side of the rotor 1 A. Like the surface of the blade 20 A at the front side of the rotor 1 A, however, the number of projections 50 per unit area on the surface at the back side of the rotor 1 A as well may decrease from the leading edge 31 A towards the trailing edge 41 A of the blade 20 A.

According to this structure for the surface of the blade 20 A, while weakening the turbulent flow occurring mainly near the region on the leading edge 31 A side of the surface of the blade 20 A at the front side of the rotor 1 A, if the turbulent flow also occurs near or advances to another surface region of the blade 20 A, such turbulent flow can also be weakened. This structure is particularly advantageous when, depending on the dimensions, the three-dimensional shape, or the like of the blade 20 A, the turbulent flow not only occurs near the region on the leading edge 31 A side of the surface of the blade 20 A at the front side of the rotor 1 A but also occurs near or advances to another surface region of the blade 20 A.

Forming the projections 50 at least on a region at the leading edge 31 A side of the surface of the blade 20 A at the front side of the rotor 1 A yields the effect of weakening the turbulent flow occurring mainly at least near the region on the leading edge 31 A side of the surface of the blade 20 A at the front side of the rotor 1 A. Therefore, while not illustrated, the projections 50 may alternatively be formed in only the region on the leading edge 31 A side of the surface of the blade 20 A at the front side of the rotor 1 A.

The dimensions and shape of each projection 50 may differ. For example, in a cross-section perpendicular to the surface of the blade 20 A (i.e. in the plane in FIG. 3 ), the cross-sectional shape of each projection 50 is an approximate Gaussian curve in the example in FIG. 3 , yet any shape may be adopted, such as a shape that is approximately a half arc or approximately rectangular, and the shapes may be identical or different. Similarly, in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A (i.e. in the plane of FIG. 2 ), the projection shape of each projection 50 is approximately circular in the example in FIG. 3 , yet any shape may be adopted, such as a shape that is approximately elliptical, approximately rectangular, approximately triangular, or the like, and the shapes may be identical or different.

In a cross-section along the width direction of the blade 20 A, as illustrated in FIG. 3 , the distribution of the projections 50 on the surface of the blade 20 A may be approximately the same as or different from a similar cross-section of the blade 20 A at each point along the width center line of the blade 20 A (the alternate long and short dash line in FIG. 1 ).

The above-described structure related to the distribution of the projections 50 on the surface of the blade 20 A is not limited to the case of the structure in a cross-section along the width direction of the blade 20 A at each point along the width center line of the blade 20 A and also includes the case of the structure when averaging the distribution of projections 50 in the cross-section at each point along the width center line of the blade 20 A.

According to Embodiment 1, when using the rotor 1 A in a wind power generator, the air resistance when the rotor 1 A rotates can be reduced in usage conditions such that laminar flow occurs, thus reducing noise and improving power generation efficiency. Similarly, when using this rotor 1 A in a water power generator, the water resistance when the rotor 1 A rotates can be reduced, thus improving power generation efficiency.

Next, Embodiment 1 of another rotor according to the present invention is described with reference to FIG. 4 . Note that a description of the structure and effects of portions that are the same as in the embodiment described with reference to FIGS. 1 to 3 are omitted. Rather, the description of the present embodiment focuses on the differences. In the Embodiment illustrated in FIG. 4 , in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, at least a portion (the entirety in the illustrated example) of the section 34 A of the leading edge 31 A of the blade 20 A extending from the inward end 33 A of the leading edge 31 A in the radial direction of the rotor 1 A to the tip 32 A of the leading edge protrusion is curved or bent (curved in the illustrated example) to be convex forward in the rotational direction RD of the rotor 1 A with respect to the second line segment L 2A connecting the inward end 33 A of the leading edge 31 A in the radial direction of the rotor 1 A and the tip 32 A of the leading edge protrusion.

According to this structure for the section 34 A of the leading edge 31 A inward in the radial direction of the rotor 1 A, the air resistance experienced by the blade 20 A can be reduced as compared to when the section 34 A extends along the second line segment L 2A .

Furthermore, in the present embodiment, at least a portion (the entirety in the illustrated example) of the section 37 A extending from the tip 32 A of the leading edge protrusion to the outward end 35 A of the leading edge 31 A of the blade 20 A in the radial direction of the rotor 1 A is curved or bent (curved in the illustrated example) to be convex backward in the rotational direction RD of the rotor 1 A with respect to the fifth line segment L 5A connecting the tip 32 A of the leading edge protrusion and the outward end 35 A of the leading edge 31 A in the radial direction of the rotor 1 A.

This structure can further reduce the air resistance as compared to when the section 37 A extends along the fifth line segment L 5A .

In the present embodiment, in the projection plane perpendicular to the central axis of rotation O of the rotor 1 A, the tip 32 A of the leading edge protrusion, with respect to the first line segment L 1A , in the leading edge 31 A of the blade 20 A may be positioned outward in the radial direction of the rotor 1 A from the peripheral edge of the hub 10 A by any distance. From the perspective of reducing air resistance, however, the tip 32 A of the leading edge protrusion with respect to the first line segment L 1A is preferably positioned outward in the radial direction of the rotor 1 A from the peripheral edge of the hub 10 A by a distance of 0.35 to 0.65 times the length B LA of the blade 20 A.

When, as in the present embodiment, at least a portion of the section 34 A extending from the inward end 33 A of the leading edge 31 A of the blade 20 A in the radial direction of the rotor 1 A to the tip 32 A of the leading edge protrusion is curved or bent to be convex forward in the rotational direction of the rotor 1 A with respect to the second line segment L 2A , then from the perspective of reducing air resistance, at least a portion (the entirety in the illustrated example) of the section 44 A extending from the inward end 43 A of the trailing edge 41 A in the radial direction of the rotor 1 A to the tip 42 A of the trailing edge protrusion is preferably curved or bent to be convex forward in the rotational direction RD of the rotor 1 A with respect to the fourth line segment L 4A .

Similarly, when as in the present embodiment at least a portion (the entirety in the illustrated example) of the section 37 A extending from the tip 32 A of the leading edge protrusion to the outward end 35 A of the leading edge 31 A of the blade 20 A in the radial direction of the rotor 1 A is curved or bent to be convex backward in the rotational direction RD of the rotor 1 A with respect to the fifth line segment L 5A , then from the perspective of reducing air resistance, at least a portion (the entirety in the illustrated example) of the section 47 A extending from the tip 42 A of the trailing edge protrusion to the outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A is preferably curved or bent to be convex backward in the rotational direction RD of the rotor 1 A with respect to the sixth line segment L 6A connecting the tip 42 A of the trailing edge protrusion and the outward end 45 A of the trailing edge 41 A in the radial direction of the rotor 1 A.

In general, when the diameter of the rotor exceeds 5 m, in addition to a vortex, a turbulent flow occurs near the leading edge of the blade when the rotor rotates. This turbulent flow might cause the lift to decrease and the fluid resistance to increase. Furthermore, when the diameter of the rotor exceeds 5 m, then as compared to when the diameter of the rotor is 5 m or less, the moving velocity of the tip portion of the blade outward in the radial direction of the rotor tends to increase. Therefore, if the tip portion of the blade has a plurality of branched portions as in the above-described Embodiment 1, the vortex near the tip portion might increase. Embodiment 2 resolves such a problem.

Embodiment 2 of the present invention is described with reference to FIG. 5 . FIG. 5 is a front view of the main parts of a rotor 1 B, according to Embodiment 2 of the present invention, for a wind or water power generator. Note that a description of the structure and effects of portions that are the same as in the embodiment described with reference to FIGS. 1 to 3 are omitted. Rather, the description of the present embodiment focuses on the differences. The rotor 1 B in FIG. 5 is used in a wind power generator. The diameter φ B of the rotor 1 B is 10 m, the number of revolutions at a wind speed of 5 m/s to 20 m/s is 10 rpm to 50 rpm, and the output is 15 kW. It is assumed that the rotor 1 B is used in a turbulent flow region with a Reynolds number exceeding 100,000 (including a transitional region between a laminar flow and a turbulent flow). The rotor 1 B according to the present embodiment, however, can be used not only in a wind power generator but also in a water power generator or another wind or water power machine. The diameter φ B of the rotor 1 B preferably exceeds 5 m. From the perspective of mechanical strength, the diameter φ B is also preferably 250 m or less and more preferably 200 m or less.

In Embodiment 2 illustrated in FIG. 5 , unlike Embodiment 1, a plurality of extended portions 60 is provided along the leading edge 31 B in a projection plane perpendicular to the central axis of rotation O of the rotor 1 B (i.e. in the plane of FIG. 5 ). Each of the extended portions 60 extends forward in the rotational direction RD of the rotor 1 B from a leading edge 31 B of a blade 20 B and tapers off forward in the rotational direction RD of the rotor 1 B. As illustrated, in the projection plane, the edge at the base of each extended portion 60 (backward in the rotational direction of the rotor 1 B) is adjacent to the leading edge 31 B, i.e. forms a portion of the outline of the leading edge 31 B.

These extended portions 60 provided on the leading edge 31 B of the blade 20 B can suppress the occurrence of turbulent flow near the leading edge 31 B of the blade 20 B. As a result, the lift of the rotor 1 B can be increased, and the air resistance can be reduced.

In the projection plane perpendicular to the central axis of rotation O of the rotor 1 B (i.e. in the plane of FIG. 5 ), the shape, direction of extension, and length of extension may differ between extended portions 60 .

The direction of extension and length of extension of an extended portion 60 refer to the direction of extension and length of extension of a line segment that connects the forward tip of the extended portion 60 in the rotational direction RD of the rotor 1 B and intermediate points between the inward end and the outward end of the extended portion 60 in the radial direction of the rotor 1 B.

In the projection plane, the shape of each extended portion 60 is approximately triangular in FIG. 5 , yet as long as the extended portions 60 taper off forward in the rotational direction RD of the rotor 1 B, they may be of any shape, such as an approximate Gaussian curve or approximately trapezoidal. In the projection plane, the extended portions 60 are not limited to being connected to each other as in the example in FIG. 5 . While not illustrated, the extended portions 60 may be separated from each other. As illustrated in FIG. 5 , not providing the extended portions 60 near a tip 32 B of the leading edge protrusion or near an inward end 33 B and an outward end 35 B of the leading edge 31 B in the radial direction of the rotor 1 B is preferable from the perspective of reducing air resistance.

Next, the blade 20 B in Embodiment 2 in FIG. 5 differs from Embodiment 1 in that the tip portion of the blade 20 B outward in the radial direction of the rotor 1 B tapers off outward in the radial direction of the rotor 1 B.

According to this structure of the tip portion of the blade 20 B outward in the radial direction of the rotor 1 B, as compared to a structure that includes a plurality of branched portions as in Embodiment 1, the occurrence of a vortex near the tip portion of the blade 20 B can be suppressed.

From the perspective of weakening the vortex that occurs near the leading edge 31 B, unlike Embodiment 1, the angle θ 1B between a second line segment L 2B connecting the inward end 33 B of the leading edge 31 B in the radial direction of the rotor 1 B and the tip 32 B of the leading edge protrusion and a fifth line segment L 5B connecting the outward end 35 B of the leading edge 31 B in the radial direction of the rotor 1 B and the tip 32 B of the leading edge protrusion is preferably 160° to 175°.

When adopting the same structure as the leading edge 31 B for the trailing edge 41 B, from the perspective of reducing the air resistance, the angle θ 2B between a fourth line segment L 4B connecting an inward end 43 B of the trailing edge 41 B in the radial direction of the rotor 1 B and a tip 42 B of the trailing edge protrusion and a sixth line segment L 6B connecting an outward end 45 B of the trailing edge 41 B in the radial direction of the rotor 1 B and the tip 42 B of the trailing edge protrusion is preferably 160° to 175°.

While not illustrated, from the perspective of weakening the turbulent flow generated near the surface of the blade 20 B, as in Embodiment 1, a plurality of the projections 50 described with reference to FIG. 3 is formed on the surface of the blade 20 B, thereby providing the surface of the blade 20 B with unevenness approximately like that of rough skin. Details on the projections 50 are the same as in Embodiment 1 and hence are omitted here.

From the perspective of reducing air resistance, the projections 50 are preferably not provided on the surface of the above-described extended portions 60 .

According to Embodiment 2, when using the rotor 1 B in a wind power generator, the air resistance when the rotor 1 B rotates can be reduced in usage conditions such that turbulent flow mainly occurs, thus reducing noise and improving power generation efficiency. Similarly, when using this rotor 1 B in a water power generator, the water resistance when the rotor 1 B rotates can be reduced, thus improving power generation efficiency.

As illustrated in FIG. 6 , the structure of the leading edge 31 A and trailing edge 41 A in the embodiment described with reference to FIG. 4 may be adopted in the rotor 1 B of the embodiment described with reference to FIG. 5 .

Next, the performance of a rotor according to the present invention and of another rotor according to the present invention were assessed by analysis, as described below. Comparative Example Rotors 1 to 3 and Example Rotors 1 to 8 each had a blade length BL A of 0.50 m, a hub radius r A of 0.10 m, and a rotor diameter φ A of 1.20 m. The analysis conditions for the rotors were as follows: wind speed of 5 m/s, aspect ratio of the blade of 6.67, frequency of 1.59 Hz, tip speed ratio of 1.20, Reynolds number of 25,000, and pitch angle of the blade of 35°.

In a projection plane perpendicular to the central axis of rotation of the rotor, the aspect ratio of the blade is the ratio of the square of the blade length to the blade area.

The frequency is the number of revolutions of the blade per second.

The tip speed ratio is the ratio of the speed of the outward end of the blade in the radial direction of the rotor to the wind speed.

The pitch angle of the blade is the angle between a plane perpendicular to the central axis of rotation of the rotor and a plane passing through the leading edge and the trailing edge of the blade.

The other particular analysis conditions for each rotor are listed in Tables 1 and 2.

Comparative Example Rotor 1

In a projection plane perpendicular to the central axis of rotation O of the rotor 1 A, the leading edge and trailing edge of the blade in Comparative Example Rotor 1 each extend linearly, i.e. along a first line segment and a third line segment connecting the inward ends in the radial direction of the rotor to the outward ends in the radial direction of the rotor.

Comparative Example Rotors 2 and 3, Example Rotors 1 to 3

In the above projection plane, the leading edge and trailing edge of the blade in each of the Comparative Example Rotors 2 and 3 and Example Rotors 1 to 3 each protrude forward in the rotational direction of the rotor with respect to the first line segment and the third line segment. Furthermore, in the projection plane, the leading edge of the blade in each of the Comparative Example Rotors 2 and 3 and Example Rotors 1 to 3 has the concavo-convex shape illustrated in FIG. 2 . In other words, the leading edge is curved to be convex backward in the rotational direction of the rotor with respect to a second line segment connecting the inward end of the leading edge in the radial direction of the rotor and the tip of the leading edge protrusion, and the leading edge is curved to be convex forward in the rotational direction of the rotor with respect to a fifth line segment connecting the tip of the leading edge protrusion and the outward end of the leading edge in the radial direction of the rotor. In the projection plane, the trailing edge of the blade in each of the Comparative Example Rotors 2 and 3 and Example Rotors 1 to 3 extends along a fourth line segment connecting the inward end of the trailing edge in the radial direction of the rotor and the tip of the trailing edge protrusion, and the trailing edge also extends along a sixth line segment connecting the tip of the trailing edge protrusion and the outward end of the trailing edge in the radial direction of the rotor.

In the projection plane, the leading edge and trailing edge of the blade in each of the Example Rotors 4 to 8 each protrude forward in the rotational direction of the rotor with respect to the first line segment and the third line segment. Furthermore, in the projection plane, the leading edge of the blade in each of Example Rotors 4 to 8 has the convexo-concave shape illustrated in FIG. 4 . In other words, the leading edge is curved to be convex forward in the rotational direction of the rotor with respect to the second line segment and curved to be convex backward in the rotational direction of the rotor with respect to the fifth line segment. In the projection plane, the trailing edge of the blade in each of Example Rotors 4 to 8 extends along the fourth line segment and along the sixth line segment.

In Tables 1 and 2, “θ 1A ” represents the angle between the second line segment and the fifth line segment. In the projection plane, “α” represents the angle between a line traversing the central axis of rotation of the rotor and the inward end of the leading edge in the radial direction of the rotor and a line traversing the central axis of rotation of the rotor and the outward end of the leading edge in the radial direction of the rotor. The “position of the tip of the leading edge protrusion” indicates the distance, along the radial direction of the rotor, from the peripheral surface of the hub to the tip of the leading edge protrusion of the blade. The distance is expressed as a multiple of the blade length BL A . The “drag torque” is the time average of the aerodynamic drag torque. A smaller value indicates smaller air resistance experienced by the blade and better rotor efficiency. The “rate of increase in drag torque” indicates the ratio of i) the value yielded by subtracting the drag torque of Comparative Example Rotor 1 from the drag torque of each rotor to ii) the drag torque of Comparative Example Rotor 1. A smaller rate of increase (a larger negative value) indicates less air resistance experienced by the blade and better rotor efficiency.

As is clear from Table 1, in Example Rotors 1 to 3 for which the tip of the leading edge protrusion is at 0.40 BL A to 0.60 BL A , the drag torque is smaller than for each of Comparative Example Rotors 1 to 3. Hence, the air resistance experienced by the blade is reduced, and the rotor efficiency is increased.

As is clear from Table 2, regardless of the position of the tip of the leading edge protrusion, in Example Rotors 4 to 8 in which the leading edge has a convexo-concave shape, the drag torque is smaller than for Comparative Example Rotor 1. Hence, the air resistance experienced by the blade is reduced, and the rotor efficiency is increased.

Therefore, it is clear that according to the rotor of the present invention, the air resistance experienced by the blade can be reduced, and the efficiency can be improved.

A rotor according to the present invention can be used in a wind or water power machine that uses a fluid force, e.g. wind power, water power, or the like, as the source of motive power, such as a wind power generator or water power generator that use a horizontal shaft rotor or the like.

1 A, 1 B: Rotor

10 A, 10 B: Hub

20 A, 20 B: Blade

21 A, 21 B: Root end of blade

31 A, 31 B: Leading edge

32 A, 32 B: Tip of leading edge protrusion

33 A, 33 B: Inward end of leading edge in radial direction of rotor

34 A, 34 B: Section of leading edge extending from inward end of leading edge in radial direction of rotor to tip of leading edge protrusion

35 A, 35 B: Outward end of leading edge in radial direction of rotor

36 A: Portion of leading edge of blade along branched portion

37 A, 37 B: Section of leading edge extending from tip of leading edge protrusion to outward end of leading edge in radial direction of rotor

41 A, 41 B: Trailing edge

42 A, 42 B: Tip of trailing edge protrusion

43 A, 43 B: Inward end of trailing edge in radial direction of rotor

44 A, 44 B: Section of trailing edge extending from inward end of trailing edge in radial direction of rotor to tip of trailing edge protrusion

45 A, 45 B: Outward end of trailing edge in radial direction of rotor

46 A: Portion of trailing edge of blade along branched portion

47 A, 47 B: Section of trailing edge extending from tip of trailing edge protrusion to outward end of trailing edge in radial direction of rotor

50 : Projection

51 A: Branched portion

60 : Extended portion

BL A , BL B : Blade length

L 1A , L 1B : First line segment

L 2A , L 2B : Second line segment

L 3A , L 3B : Third line segment

L 4A , L 4B : Fourth line segment

L 5A , L 5B : Fifth line segment

L 6A , L 6B : Sixth line segment

O: Central axis of rotation of rotor

R, S: Branch starting position

RD: Rotational direction

d: Diameter of projection

h: Height of projection

l 1 , l 2 : Tangent line

r A , r B : Radius of hub

φ A , φ B : Diameter of rotor

θ 1A , θ 2A , θ 1B , θ 2B : Angle